There's all sorts of quirks for anything published before that rule got standardised more-or-less worldwide, but in general 1930-1945 is still like a legal grey area that can be challenged in court and you should be good to go for anything published before that. And don't get me even started on posthumous publications, that's a whole different can of worms where a family member might claim some contribution (like for example Anne Frank's father), pushing the copyright further to the life of the author + life of that family member + 70.